The objective of this study is to formulate quantitative descriptions of the relationships between alterations of in vivo mechanical loading histories and local cortical bone tissue remodeling. The cyclic strain and stress patterns of the midshaft of the normal canine radius and femur will be determined using multiple in vivo strain gage implantations. Also using in vivo strain gages, the change in loading histories in the radius will be established after 1) distal ulna resection (radius overload model), and 2) cast immobilization and recovery (radius immobilization and recovery model). The data will be analyzed and processed on a computer using beam theory and finite element mathematical models. The change in loading histories in the dog femur after rigid plate fixation will be determined using mathematical models and experimentally determined bone and bone/plate sectional properties. The mathematical computations will be verified using additional in vivo gages implantation on plated femora. Metal plates, metal plates with a porous ingrowth surface, and UHMWP plates will be used. This investigation will elucidate the structural behavior of the normal human acetabulum and examine the alterations in acetabular mechanics after total hip replacement, surface replacement, and femoral endoprosthesis hip arthroplasty. The project will involve direct mechanical testing of cadaver specimens and the generation of 2-D and 3-D finite element models for numerical stress analysis.